Air foil fan

ABSTRACT

A multibladed rotatable fan, for cooling motors and the like within a confined housing, having air foil blades designed to produce maximum air flow axially within the limited crosssectional area of the housing and discharge the air at an angle from the housing while maintaining a minimum noise level and reduced turbulence at high speeds within the housing.

United States Patent Inventor Michael Adajian Canton, Conn. Appl. No. 853,783 Filed Aug. 28, 1969 Patented Apr. 20, 1971 Assignee Dynamics Corporation of America New York, N.Y.

AIR FOIL FAN 9 Claims, 5 Drawing Figs.

US. Cl 415/213, 416/243, 310/62 Int. Cl F04d 7/00 Field ofSearch 415/213; 416/223, 243; 310/58, 62

References Cited UNITED STATES PATENTS 1,271,622 7/1918 Searles 416/243 1,370,284 3/1921 Carlson 416/243 1,957,237 5/1934 Upson 416/243 2,072,322 3/1937 Upson 416/243 2,243,189 5/1941 Brannan... 416/243 2,957,621 10/1960 Haims 416/223 3,175,594 3/1965 Jepson et a1. 310/62 Primary Examiner-C. J. Husar Attorney-Harbaugh and Thomas ABSTRACT: A multibladed rotatable fan, for cooling motors and the like within a confined housing, having air foil blades designed to produce maximum air flow axially within the limited cross-sectional area of the housing and discharge the air at an angle from the housing while maintaining a minimum noise level and reduced turbulence at high speeds within the housing.

AIR FOIL FAN BAGKGROUND OF THE INVENTION Fans of the centrifugal and disc or propeller type are well known and operate at low pressures in the order of inches water gauge or less, although some heavy duty types operate at pressures up to inches water gauge. Centrifugal fans are generally suitable for ventilating work where ducts are involved or air is required for drying or forming suspensions in an air stream or removing fumes and dust from working spaces. Where large volumes of air are handled at low pressures, as in exhausting an open space, or cooling motors, etc., the propeller or disc fan is known to be more efficient. The operating efiiciencies of most fans lie in the range of 40 to 65 percent. The operating pressure or impact pressure or head of a fan is the sum of the static pressure and the velocity head of the air leaving the fan, expressed in inches of water gauge or ounces per square inch. Thus, a head of 1 inch water equals a head of 69.3 feet air, or 1 ounce per square inch equals 1.732 inches of water. It is highly desirable that the perfonnance of a fan be maintained at its maximum efiiciency within the confines of housings and the like. However this goal is not always attained, particularly at high operating speeds in the order of 10,000 r.p.m. or higher.

There are several ways of evaluating the performance of a fan including determinations of total pressure, air horsepower, mechanical efficiency and pressure efficiency. The performance of a fan varies with changes in conditions such as temperature, speed and air density and general data as to performance is set forth on assumed standard conditions, such as 70 F., 29.92 inches barometric pressure, of 68 F., and 50 R.H. Corrections must be made for variations from assumed standard conditions in evaluating fan performance. Thus, when the speed varies: the capacity varies directly as the speed ratio, the pressure varies as the square of the speed ratio, and the horsepower varies as the cube of the speed ratio. However, when the temperature of the air varies: the horsepower and pressure vary inversely as the absolute temperature (speed and capacity being constant) and when the density of the air or gas varies: the horsepower and pressure vary directly as the density (speed and capacity being constant). The presence of a housing and high-speed operation further complicate these factors.

The design of the fan rotor which may be with forward, curved or backward-curved blades and with radial or straight blades has a decided influence on the aforesaid performance values and the effect of blade curvature on fan characteristics has been studied for centrifugal fans. Little performance information is available for high-speed disc'or propeller-type fans. Practically no information is available regarding the effects of rotational speeds on noise levels or the adverse combined effects of housings, air passageways and the like that are necessary parts of motor housings and other confining walls within which a high-speed fan may be required to operate.

Accordingly, the design engineer generally makes all such passageways as large as possible considering some of the operating conditions of the motor with regard to the strength of materials but without too much regard to fan speed or efficiency. A fan is selected because it will move air and the housing is designed around the fan and motor to allow air circulation. If the motor doesn't overheat and the device has the required work characteristics the design is accepted.

However, the environment of an electric motor changes during use, exposed metal surfaces corrode, and dust and grease may collect on the heat-dissipating surfaces, greatly lowering their efficiency. Intakes may become obstructed by objects placed adjacent the motor housing. The crosssectional area available to air flow may be suddenly or gradually reduced or air flow impeded by such obstructions and accumulations. The tendency is to permit radial escape of air from the tops or ends of the blades of the fan without due regard for the noise level and to provide enlarged side openings and other passages to reduce the flow velocity to counteract the noise level so produced.

SUMMARY OF THE INVENTION In accordance with this invention a high-speed, combination axial and centrifugal fan is provided with air foil blades in combination with a housing for a motor or the like having an end bell enclosure with radial exhaust openings in the circular wall thereof contiguous to the exhaust side of the blade. The shape of the fan blade, within the end of the housing is designed to force the major portion of the air divergingly outwardly resulting in a cone-shaped discharge from the end of the motor with minimum redirection of flow within the end bell at approximately 45 which has been found to assist in the flow and turnaround of air within the housing outside the bell, the forced air being compressed as it leaves the blades and rapidly expanding with a radial flow component as it enters the housing. The air flow is laminar and less turbulent within the motor housing and the noise level is reduced to a minimum though the rotational speeds read 18,000 r.p.m. or more.

The fan of this invention has a number of characteristics including:

l. coplanar outer leading edges on the blades that depend toward the plane of the hub;

2. the leading edges of adjacent blades are circumferentially offset about 45 from each other;

3. an even number of blades is used with the leading edges of pairs of the blades being circumferentially (or diametrically) opposite; and

4. the pitch of the blades is such that the ratio of the depth of the trailing curved surface, forming the centrifugal air foil component, at the plane of the hub to the depth of the forward curved surface forming the balance of the air foil, at the same plane through the blade, is about 2:1 and preferably in the range of about 38:20; or about 0380:0207 inches for a 2 /2- inch fan;

5. the air is confined to flow axially and circularly until it approaches the trailing edges of the blades which overlap the radial exhaust openings appreciably whereupon they centrifugally expand conically in and beyond the exhaust openings.

DESCRIPTION OF THE DRAWINGS An illustrated embodiment of the invention is shown in the drawings herein:

FIG. 1 is a side perspective view of the housing of a highspeed liquidizer partially cut away to show the interior and illustrating the receptacle in phantom;

FIG. 2 is a fragmentary view in vertical section of the housing or base of FIG. 1 to show the essential parts forming the environment of the fan of this invention and showing by means of arrows the air flow therethrough;

FIG. 3 is a top plan view of the fan of this invention;

FIG. 4 is a side or edge perspective view of the fan of this invention; and

FIG. 5 is an end view of a blade of the fan ofthis invention.

THE PREFERRED EMBODIMENT Referring to FIG. 1 the liquidizer base 10 is illustrative of a molded plastic stand to contain an electric motor controlled by the switch panel 12 through manipulation of the buttons 14 adapted to connect the power source thereto and produce different driving speeds upon the workpiece or coupling 16, the latter being representative of any element that is rotated by the motor for the purpose of stirring, grinding, mixing, blending, etc. as may occur in a kitchen, work shop, laboratory or the like. In this instance, the receptacle 18 is provided with a mating coupling (not shown) attached through the bottom wall on a shaft to a cutter blade adapted to liquidize or blend the contents of the receptacle as is known in the art.

Referring to FIG. 2 in more detail, the base is shown to have supporting feet on the bottom wall 22 which raise the base above the supporting surface 24 a sufficient distance to provide total access of air from all directions within the surrounding space 26 defined therebetween. Aside from the feet 20, which are in the form of molded rubber plugs held within the recesses of the molded flanges 28, the space 26 is particularly unobstructed.

The bottom wall 22 has an integral spider bracket 30 with connected spoke members 32 of the housing 34 which supports the motor 36, the connecting power and switch wires of which are omitted for simplicity. The spokes 32 occupy about only 20 percent of the end opening of the housing 34 and define therebetween the openings 46 for the passage of air into the annular space 44. The inner wall surface 40 is smooth and unobstructed ahead and beyond the stator and behind the pole portions where the stator is segmentally relieved. A pair of mounting bolts 42, one of which is shown, extend longitudinally in the direction of flow and engage a supporting boss (not shown) at the top end of the motor. The wall surface 40 and the motor 36 define a generally annular elongated air passage 44 about and through the motor for intimate and moving contact with the stator and armature cores and the windings thereon.

The base 10 is provided with an integral top collar 48 to receive the bottom of the receptacle 18 and has the intermediate wall 50 with a central embossment 52 carrying the bearing member 54 provided with the radial spokes 56 that extend to the periphery of the wall 34 at selected points. The top edge 58 of the wall 34 has a series of openings 60 therearound and offset from the spokes 56. The shaft 62 of the motor 36 has the central hub member 64 press-fitted thereon and the latter is swaged to the collar 66 of the fan 70. The shaft extends through the embossment 52 where it carries the drive coupling member 72. At the bottom of the motor assembly the shaft 62 is carried in the thrust bearing 74. A central foot 20 can be provided at the bottom of the motor, held by the yoke embossment 75. The collar 48 has the internal lugs 76 which engage with peripheral recesses in the receptacle 18 so that it seats therein in nonrotational relationship.

Referring to FIGS. 3 and 4 the fan 70 is shown to comprise the hub plate member 66 with the attached collar 64, and is provided with the peripheral rolled raised embossment 78 having the radial blades 80 extending therefrom. The blades 80 have straight leading edges 82 interrupted by the inner raised base 04 at the juncture with the embossment 78. The tips or outer edges 86 of the blades 80 were segments of a circle in their flat condition in the blank from which they were cut and upon press-forming into the air foil shape shown become slightly arcuate. The trailing edge 88 of each blade is uptilted to form the curved air foil pocket 90 therein defined by the curving intersection of the essentially triangular flat upstanding plate portion 92 and outwardly and downwardly directed curved plate portion 94 joined at the trailing curve of the pocket 90. The leading edge 82 of any one blade 80 is diametrically opposite the leading edge, i.e., edge 82' of an opposite blade. This offsets each opposite blade from the other around the periphery of the embossment 78. This also places the outer curved tip 86 of the opposing blades on a diameter D-D of the fan and offsets the trailing edges 88 of opposing blades in such a manner that they are substantially parallel to each other and the leading outer comer 98 of any one blade lies in the plane of the trailing edge of the opposite blade. The spaces 99 between the respective blades 80 are segmental in shape. The top trailing comers 100 of the blades are in a plane above the plane of the tips 98.

This relationship of the parts of the fan is further defined by the planar dimensions A and B in FIG. 3. The dimension A is between the plane of the tips 100 of the fan and the bottom or inner plane of the hub 66. The dimension B is between the plane of the hub 66 and the bottom or inner (in relation to the motor) plane of the plate portions 94 or the tips 98. The

relationship of AB is preferably about 2:1 and preferably about 3.8220. In a fan about 2.531 inches in outside diameter the distance A is about 0.380 inch and B is about 0.207 inches one embodiment.

Referring to FIG. 2 it is seen that the fan 70 is positioned within the wall 34 so that the tips 86 are spaced as at 101 therefrom by a fairly close tolerance of about one thirtysecond to one sixteenth of an inch and the top or outer (in relation to the motor) tips 100 are slightly above the edges 58 of the openings 60.

This placement has been found to be essentially desirable to high-speed noise-minimized operation of the fan 70 in the housing 34. Thus, the planar dimension A of the fan 70 is close to the plane of the edges 58 of the exit openings thereabout.

The relationship of the parts forming the air foil pocket 90 is further shown in FIG. 5 wherein the x-y axis represents the plane of the tips or corners 98 and 100 of a blade and the axes m-m and p-r are drawn normal tov each other and intersect at center of radius of the pocket 92. The two angles 0 are equal and are about 45. The area of the flat portion 92 is about twice that of the area of the flat portion 94 and the remaining curved pocket is about the same as that of portion 94.

The fan blade can be molded from rigid high-strength plastic or press-formed from a flat sheet metal blank. Larger fans can be formed than the fan illustrated. The fans can have a minimum of two blades and the number of blades can be an odd or even number, except that if an odd number of blades is used the relationship along the line D-D cannot be maintained. Thus, in the preferred embodiment an even number of blades is used.

During operation of the fan of this invention, the air is drawn as indicated by the broken line arrows 102 into the opening 46, through the annular passage 44, between the segmental spaces 99 to be caught in the air foil pocket 90 and moved rapidly at an angle of about 45 in a cone-shaped pattern against the wall 50 where it is deflected back down within the housing 10, through the outer annular passage 104, surrounding the housing 34, and through a plurality of exit slits 106. The air flow is maximum axially about the motor 36 at all times and essentially laminar therethrough with no turbulence. With the exit radially spaced openings 60 above the plane of the tips the operation of the fan is noise-free even at l8,000 r.p.m.

lclaim'.

1. A propeller-type fan comprising:

a hub member adapted to be affixed to a rotatable shaft,

a plurality of fan blades extending radially from said hub member,

said blades each having a leading edge, a trailing edge and an outer edge,

said blades each comprising an air foil facing in the direction of rotation,

said air foil being defined by an essentially planar upstanding portion, a curved intennediate portion and a leading flat portion;

the ratio of the respective planar areas of said upstanding portion and said leading flat portion being about 2:1

2. A propeller-type fan in accordance with claim 1 in which:

said respective planar portions of said air foil join into said curved intermediate portion to form a curved surface area about equal to the planar area of the leading flat portion at any selected cross section of a blade.

3. A propeller-type fan in accordance with claim 1 in which:

the the leading edge of any one blade is diametrically opposite the leading edge of an opposite blade.

4. A propeller-type fan in accordance with claim 1 in which:

the plane of the following edge of a blade intersects the tip of the leading edge of an opposite blade.

5. In combination with an open-ended tubular housing a propeller-type fan comprising:

a hub member adapted to be affixed to a rotatable shaft,

a plurality of fan blades extending radially from said hub member,

said blades each having a leading edge, and a trailing edge and an outer edge intersecting in a raised tip,

said blades each comprising an air foil facing in the direction of rotation,

said air foil being defined by an essentially planar upstanding portion, a curved intermediate portion and a leading flat portion,

the ratio of the respective planar areas of said upstanding portion and said leading flat portion being about 2:1,

said fan being rotatably mounted within said housing with the plane of the raised tips spaced inwardly from said open end of said housing.

6. The combination called for in claim 5 in which:

said rotatable shaft is driven by an electric motor,

said fan is mounted on said shaft between an end of said motor and an end wall of said housing,

said open end of said housing comprising a side opening radially spaced from said shaft and extending to said end wall, and

said raised tips of said air foil are essentially coplanar with the bottom edge of said side opening.

7. The combination called for in claim 5 in which:

said respective planar portions of said air foil join into said curved intermediate portion to form a curved surface area about equal to the planar area of the leading flat portion at any selected cross section of a blade.

8. The combination called for in claim 5 in which:

the leading edge of any one blade is diametrically opposite the leading edge of an opposite blade.

9. The combination called for in claim 5 in which:

the plane of the following edge of a blade intersects the tip of the leading edge of an opposite blade. 

1. A propeller-type fan comprising: a hub member adapted to be affixed to a rotatable shaft, a plurality of fan blades extending radially from said hub member, said blades each having a leading edge, a trailing edge and an outer edge, said blades each comprising an air foil facing in the direction of rotation, said air foil being defined by an essentially planar upstanding portion, a curved intermediate portion and a leading flat portion; the ratio of the respective planar areas of said upstanding portion and said leading flat portion being about 2:1.
 2. A propeller-type fan in accordance with claim 1 in which: said respective planar portions of said air foil join into said curved intermediate portion to form a curved surface area about equal to the planar area of the leading flat portion at any selected cross section of a blade.
 3. A propeller-type fan in accordance with claim 1 in which: the the leading edge of any one blade is diametrically opposite the leading edge of an opposite blade.
 4. A propeller-type fan in accordance with claim 1 in which: the plane of the following edge of a blade intersects the tip of the leading edge of an opposite blade.
 5. In combination with an open-ended tubular housing a propeller-type fan comprising: a hub member adapted to be affixed to a rotatable shaft, a plurality of fan blades extending radially from said hub member, said blades each having a leading edge, and a trailing edge and an outer edge intersecting in a raised tip, said blades each comprising an air foil facing in the direction of rotation, said air foil being defined by an essentially planar upstanding portion, a curved intermediate portion and a leading flat portion, the ratio of the respective planar areas of said upstanding portion and said leading flat portion being about 2:1, said fan being rotatably mounted within said housing with the plane of the raised tips spaced inwardly from said open end of said housing.
 6. The combination called for in claim 5 in which: said rotatable shaft is driven by an electric motor, said fan is mounted on said shaft between an end of said motor and an end wall of said housing, said open end of said housing comprising a side opening radially spaced from said shaft and extending to said end wall, and said raised tips of said air foil are essentially coplanar with the bottom edge of said side opening.
 7. The combination called for in claim 5 in which: said respective planar portions of said air foil join into said curved intermediate portion to form a curved surface area about equal to the planar area of the leading flat portion at any selected cross section of a blade.
 8. The combination called for in claim 5 in which: the leading edge of any one blade is diametrically opposite the leading edge of an opposite blade.
 9. The combination called for in claim 5 in which: the plane of the following edge of a blade intersects the tip of the leading edge of an opposite blade. 